1. Field of the Invention
This invention relates generally to a method and apparatus for cementing production tubing in a multilateral borehole, and more specifically to such a method and apparatus wherein cement used for lining the borehole does not block adjacently disposed laterals.
2. Background of the Invention
Directional drilling has recently become increasingly important in the oil industry as a cost effective alternative to vertical drilling because this technique significantly improves production. To further increase production, one or more lateral wellbores may be drilled, with the greatest production being achieved from a multilateral well. Due to this increased dependence on horizontal wells, problems with lateral completion have been a growing concern.
Multilateral boreholes are commonly used to increase the production from a defined hydrocarbon production zone. The term “lateral,” as used herein and in the claims, means a branch borehole extending generally radially outwardly from a pilot, or main, well borehole. The radially outwardly extending branches may be horizontally oriented or erected at a diagonal angle with respect to the axis of the main well borehole. Although not as common, the term “lateral” also includes a lateral mixed in from a preexisting lateral-that is, a lateral may be a branch off of an earlier-formed lateral.
Heretofore a problem with cementing multilateral boreholes has been that cement used to line the borehole can extrude backwardly through the borehole and block the junction of adjacent laterals with the main well borehole. For example, in the parent application of this application, a liner hanger for the production tubing extending into the lateral was placed in the main production casing of the primary wellbore and cement injected for lining around the production tubing in the lateral would fill the lateral and portion of the main well borehole up to the vicinity of the liner hanger. When multilateral boreholes are formed, if cement extrudes backwardly through the lateral being lined into the junction of an adjacent lateral, that cement will plug the junction and prevent production tubing from later being placed and cemented into the adjacent lateral.
The present invention is directed to overcoming the problem outlined above. It is desirable to have a method and apparatus for cementing production tubing into a lateral without blocking adjacently-formed laterals with the cement lining material. It is also desirable to have such a method and apparatus wherein the liner hanger is positioned in the lateral being lined and the cement lining prevented from backflowing any significant amount beyond the hanger.